Such cutting inserts are generally provided with curved corners. U.S. Pat. No. 6,196,771 discloses a cutting insert having first and second side faces. Each side face includes a pair of minor cutting edges at each corner of the insert. The two minor cutting edges are located on two opposing sides of a corner bisector B, together forming an obtuse inner angle of about 170°, and are mirror-imaged about the bisector B. Two major cutting edges intersect respective ones of the minor cutting edges whereby each major cutting edge and its associated minor cutting edge together form a cooperating pair of cutting edges. There are two such cooperating pairs at each corner of each side face, whereby the insert has at least sixteen cooperating pairs. During a milling operation the insert is oriented so that only one cutting corner engages a work-piece, and only one of the cooperating pairs of cutting edges of that cutting corner is operative. Only half of the major cutting edge of each cooperating pair is effective. The minor cutting edge of the operative cooperating pair of cutting edges constitutes a wiper edge, by being arranged parallel to the surface of the work-piece, that is perpendicularly to an axis of rotation of a milling tool in which the cutting insert is mounted.
A drawback of these known inserts is that the minor cutting edge of each cooperating pair has a constant setting angle during the machining of the work-piece. Positioning deviation of the cutting insert relative to a cutter body of a milling cutter in which the cutting inserts are mounted, or axial bending of the milling cutter (which may occur under demanding machining conditions) may result in either a wiper corner adjacent the main cutting edge, or a wiper corner distal the main cutting edge of the cooperating pair cutting into the work-piece face, and thereby marring the face of a work-piece being milled.
U.S. Pat. No. 5,032,049 discloses an indexable cutting insert for face milling of engine blocks of cast iron. The insert has two opposing, substantially identical, generally square-shaped upper and lower surfaces which are perpendicularly connected by four side surfaces. Two adjacent side surfaces connect to each other via a smoothly rounded corner. The radius of the corner R is ¼ to ⅛ of a length X of the insert, and therefore the setting angle gets close to zero degrees during machining of the engine block when the insert gets close to the border line of the work piece. The corner of the cutting insert serves in machining the shoulder of a work-piece, as well as in finishing the face of the work-piece during the last pass of the milling cutter.
It is an object of the present invention to provide an improved cutting insert. This object is attained with the subject matter in accordance with the claims.